Q3Electrical Machines II

When a single-phase alternating current flows through a single winding fixed on the stator, it generates a magnetic field. Because the physical position of the coil is fixed, the spatial axis of the resulting magnetic field is also fixed (stationary in space).

However, because the current is alternating sinusoidally with time ($i(t)=I_{m}sinomegat$), the strength of the magnetic flux also alternates sinusoidally, growing to a maximum North pole, shrinking to zero, and then reversing to a maximum South pole.

This is known as a Pulsating Magnetic Field. It acts as if the magnetic poles are breathing in and out along a fixed line, rather than rotating. By Double Revolving Field Theory, this pulsating field is equivalent to two separate fields rotating in opposite directions.